Screaming Bogey of Strathtully

The Screaming Bogey of Strathtully was a Scottishboggart who fed on the fears of the local muggles to a point that it had become an elephantine black shadow with glowing white eyes. Eventually, Lyall Lupin was able to trap the boggart in a matchbox.[1]

Behind the scenes

This shows a clear example that if a Boggart enjoys life and fears too much it might grow to something like this and actually do physical damage to its surroundings.